ANSWERS TO REVIEW QUESTIONS – CHAPTER 01
1. What is an atom? What are components of an atom? (p. 17)
An atom is the smallest piece or bit of matter that is stable under our familiar conditions of temperature
and pressure. The components of an atom depend on how hard you smash it up but at moderate
energies we get three kinds of particles—negatively charged electrons, positively charged protons and
neutrons that have no charge and do not interact with electrostatic fields. When functioning as an atom,
the proton and neutron are found together in the nucleus with the electrons arranged in standing wave
patterns in the space around the nucleus.
2.
Each element has an atomic number and an atomic weight. For example, oxygen has an
atomic number of 8 and an atomic weight of 16. Explain the difference between these terms.
(p. 17)
The atomic number specifies the number of positively charged protons in the nucleus, and therefore the
number of negatively charged electrons in the neutral atom. The mass of the atom is very low (e.g. a
hydrogen atom weighs 1.7 × 10–27 kg) so the atomic mass unit (the Dalton, defined as one-twelfth of
the mass of a carbon-12 atom) is used as a comparative mass. The atomic mass is the weight of that
atom relative to the Dalton. Effectively, the protons and neutrons are responsible for more than 99.9%
of the mass of an atom.
3.
Draw the atomic structures of several water molecules. Indicate on your diagram the forces
holding the atoms together and the forces between the molecules in liquid water. Name the
two types of bonding and describe the difference between them. (p. 19)
The sharing of electrons between the oxygen and hydrogen atoms, when they approach each other,
generates forces holding the atoms together in a molecule. Generally these are known as intramolecular
forces. The boiling and melting points of water are a function of how well water molecules stick
together due to intermolecular forces. These are understood in the form of van der Waals forces, the
attraction between permanent dipoles and hydrogen bonding.
Several water
molecules
Intermolecular
forces
Intramolecular
forces
4. How does a buffer work and why are they important in cells? (p. 25)
A buffer consists of a weak acid in solution with its conjugate base, i.e. HCO 3– and CO32–. A buffer
resists changes in pH by neutralising the acid or base that is added to the buffer solution. If H + is added
to the above buffer, carbonate will be converted to bicarbonate, effectively removing the H +.
5.
If the internal pH of a muscle cell changes from 7.4 to 6.4 during contraction, what is the
relative increase in H+ ion concentration? (p. 25)
pH is a measure of the H+ concentration in a solution in which decreasing pH indicates increasing
acidity and increasing pH indicates increasing alkalinity. pH is expressed as the concentration of
hydrogen ions (protons) [H+] mol L–1 and is calculated by taking the negative logarithm (to base 10) of
the hydrogen ion concentration (–log10 [H+]). Because the scale is logarithmic (base 10), each one point
change on the pH scale is equivalent to a 10-fold change in H+ concentration. The mid-point on the
scale is 7, the pH of pure water (neutral). Thus in the example in this question there has been a 10-fold
decrease in H+ ion concentration and the cell pH has changed from slightly alkaline to slightly acidic